Novel alginate gel microspheres produced by impinging aerosols for oral delivery of proteins

Lysozyme and insulin were encapsulated in alginate gel microspheres using impinging aerosols method. High loadings of around 50% weight/dry microspheres weight were obtained with encapsulation efficiencies of at least 48%. Environmental scanning electron microscopy revealed smooth spherical hydrated microspheres (30–60?µm) in diameter. No lysozyme or insulin release was measured in simulated gastric fluid (HCl, pH 1.2, 37°C). Total insulin release occurred in simulated intestinal fluid (SIF; phosphate buffer saline, pH 7.4, 37°C) in 8?h following 2?h incubation in SGF and was found to retain 75% activity using the ARCHITECT® assay. Lysozyme was released completely in SIF in 10?h following 2?h incubation in SGF and was found to exhibit at least 80% bioactivity using the Micrococcus lysodeikticus assay. The absence of protein release in HCl and the retention of high levels of biological activity demonstrate the potential of alginate gel microspheres, for improving oral delivery of biopharmaceuticals.     

A novel impinging aerosols method for production of propranolol hydrochloride-loaded alginate gel microspheres for oral delivery

Propranolol hydrochloride was directly encapsulated in alginate gel microspheres (40-50?μm in diameter) using a novel method involving impinging aerosols of CaCl(2) cross-linking solution and sodium alginate solution containing the drug. Microspheres formulated using 0.1?M CaCl(2) exhibited the highest drug loading (14%, w/w of dry microspheres) with 66.5% encapsulation efficiency. Less than 4% and 35% propranolol release occurred from hydrated and dried microspheres, respectively, in 2?h in simulated gastric fluid (SGF). The majority of the drug load (90%) was released in 5 and 7?h from hydrated and dried microspheres, respectively, in simulated intestinal fluid (SIF). Prior incubation of hydrated microspheres (cross-linked using 0.5?M CaCl(2)) in SGF prolonged the time of release in SIF to 10?h, which has implications for the design of protocols and correlation with in?vivo release behaviour. Restricted propranolol release in SGF and complete extraction in SIF demonstrate the potential of alginate gel microspheres for oral delivery of pharmaceuticals.     

Diffusion loading and drug delivery characteristics of alginate gel microparticles produced by a novel impinging aerosols method

Microencapsulation of a hydrophilic active (gentamicin sulphate (GS)) and a hydrophobic non-steroidal anti-inflammatory drug (ibuprofen) in alginate gel microparticles was accomplished by molecular diffusion of the drug species into microparticles produced by impinging aerosols of alginate solution and CaCl₂ cross-linking solution. A mean particle size in the range of 30–50 µm was measured using laser light scattering and high drug loadings of around 35 and 29% weight/dry microparticle weight were obtained for GS and ibuprofen respectively. GS release was similar in simulated intestinal fluid (phosphate buffer saline (PBS), pH 7.4, 37°C) and simulated gastric fluid (SGF) (HCl, pH 1.2, 37°C) but was accelerated in PBS following incubation of microparticles in HCl. Ibuprofen release was restricted in SGF but occurred freely on transfer of microparticles into PBS with almost 100% efficiency. GS released in PBS over 7?h, following incubation of microparticles in HCl for 2?h was found to retain at least 80% activity against Staphylococcus epidermidis while Ibuprofen retained around 50% activity against Candida albicans. The impinging aerosols technique shows potential for producing alginate gel microparticles of utility for protection and controlled delivery of a range of therapeutic molecules.     

Formation of alginate microspheres produced using emulsification technique

This study investigated the formative process of alginate microspheres produced using an emulsification technique. The alginate microspheres were produced by cross-linking alginate globules dispersed in a continuous organic phase using various calcium salts: calcium chloride, calcium acetate, calcium lactate and calcium gluconate. The size, shape, drug content and Ca2+ content of the microspheres were evaluated. The tack, viscosity and pH of the calcium salt solution and percentage of Ca2+ partitioned into the organic phase were determined. Microscopic examination of the test emulsion at various stages of the emulsification process was also carried out. The propensity of cross-linking reaction was found to be dependent on successful collision between alginate and calcium salt globules. Examination of the characteristics of microspheres indicated that the formed microsphere was a resultant product of alginate globule clustering. The growth propensity of microspheres was promoted by the higher rate and extent of cross-linkage which was governed by the pH, tack and/or Ca2+ content of the cross-linking solution, as well as the dissociation constant and diffusivity of the calcium salt. Overall, the amount of free Ca2+ cross-linked with alginate in the formed microspheres was in the following order: calcium acetate > calcium chloride + calcium acetate > calcium chloride + calcium gluconate; calcium chloride + calcium lactate > calcium chloride. In microencapsulation by emulsification, the mean size of the microspheres produced can be modified by varying the tack, pH and Ca2+ content of the cross-linking solution and through the use of a combination of calcium salts. The shape of the microspheres produced was, nonetheless, unaffected by the physicochemical properties of the cross-linking solution.     

Formation of alginate microspheres produced using emulsification technique

This study investigated the formative process of alginate microspheres produced using an emulsification technique. The alginate microspheres were produced by cross-linking alginate globules dispersed in a continuous organic phase using various calcium salts: calcium chloride, calcium acetate, calcium lactate and calcium gluconate. The size, shape, drug content and Ca²⁺ content of the microspheres were evaluated. The tack, viscosity and pH of the calcium salt solution and percentage of Ca²⁺ partitioned into the organic phase were determined. Microscopic examination of the test emulsion at various stages of the emulsification process was also carried out. The propensity of cross-linking reaction was found to be dependent on successful collision between alginate and calcium salt globules. Examination of the characteristics of microspheres indicated that the formed microsphere was a resultant product of alginate globule clustering. The growth propensity of microspheres was promoted by the higher rate and extent of cross-linkage which was governed by the pH, tack and/or Ca²⁺ content of the cross-linking solution, as well as the dissociation constant and diffusivity of the calcium salt. Overall, the amount of free Ca²⁺ cross-linked with alginate in the formed microspheres was in the following order: calcium acetate > calcium chloride + calcium acetate > calcium chloride + calcium gluconate; calcium chloride + calcium lactate > calcium chloride. In microencapsulation by emulsification, the mean size of the microspheres produced can be modified by varying the tack, pH and Ca²⁺ content of the cross-linking solution and through the use of a combination of calcium salts. The shape of the microspheres produced was, nonetheless, unaffected by the physicochemical properties of the cross-linking solution.     

Polyelectrolyte-coated alginate microspheres as drug delivery carriers for dexamethasone release

Alginate microspheres loaded with dexamethasone were prepared by the droplet generator technique. Important parameters affecting drug release, including initial drug content, the type of polyelectrolyte coating, and a combination of different ratios of coated and uncoated microspheres were investigated to achieve in vitro dexamethasone delivery with approximately zero order release kinetics, releasing up to 100% of entrapped drug within 1 month, wherein dexamethasone released at a steady rate of 4.83 μg/day after an initial burst release period. These findings imply that these polyelectrolyte-coated alginate microspheres show promise as release systems to improve biocompatibility and prolong lifetime of implantable glucose sensors.     

Composite alginate microspheres as the next-generation egg-box carriers for biomacromolecules delivery

Introduction: Alginate microspheres are versatile tools for the delivery of a wide range of therapeutic biomacromolecules. This naturally occurring biopolymer has many unique properties making it an ideal candidate for tailoring with different composites of polymers leading to the formation of strong complexes for a broad range of applications.

Areas covered: This article overviews various types of composite alginate microspheres, methods of preparation, new technologies available, physico-chemical characteristics, controlled release profiles, applications and the future directions of composite alginate microsphere delivery system for biomacromolecules.

Expert opinion: Composite alginate microsphere systems are the ideal carriers for controlled delivery applications because of their ability to encapsulate a myriad of therapeutic drugs, proteins, enzymes, DNA, antisense oligonucleotides, vaccines, growth factors and chemokines as well as the ease of processing, mechanical properties, biocompatibility, high bioavailability, controlled release rates, stability, suitability for different administration modes, targeted/localized delivery of different agents and large-scale production with cost-effectiveness. This article presents updated information of applying microalginate-based technologies and tools in the biomedical field which will benefit research scientists and clinical physicians or biopharmaceutical industries keen in the development of application-based new therapeutic and diagnostic strategies for various diseases. Furthermore, this technology will play more important roles in biosensors, vaccination, tissue engineering, cancer chemotherapeutics and stem cell research.     

Novel tamarind seed polysaccharide-alginate mucoadhesive microspheres for oral gliclazide delivery: in vitro-in vivo evaluation

Novel tamarind seed polysaccharide (TSP)-alginate mucoadhesive microspheres were prepared using TSP and alginate as blend in different ratios with different calcium chloride (CaCl(2)) concentration as a cross linker by ionotropic gelation. The prepared microspheres were of spherical shape having rough surfaces, and average particle sizes within the range of 752.12 ± 6.42 to 948.49 ± 20.92 μm. The drug entrapment efficiency of these microspheres were within the range between 58.12 ± 2.42 to 82.78 ± 3.43% w/w. Fourier transform infrared (FTIR) studies indicated that there were no reactions between gliclazide, and polymers (TSP, and sodium alginate) used. Different formulations of gliclazide loaded TSP-alginate microspheres showed prolonged in vitro release profiles of gliclazide over 12 hours in both stomach pH (pH 1.2), and intestinal pH (pH 7.4). It was found that the gliclazide release in gastric pH was comparatively slow and sustained than intestinal pH. These TSP-alginate microspheres also exhibited good mucoadhesivity. The in vivo studies on alloxan-induced diabetic rats (Animal Ethical Committee registration number: IFTM/837ac/0160) demonstrated the significant hypoglycemic effect of selected formulation of TSP-alginate mucoadhesive microspheres containing gliclazide on oral administration. This developed gliclazide loaded new TSP-alginate mucoadhesive microspheres may be very much useful for prolonged systemic absorption of gliclazide for proper maintaining blood glucose level and advanced patient compliance.     

Use of floating alginate gel beads for stomach-specific drug delivery.

Two types of alginate gel beads capable of floating in the gastric cavity were prepared. The first, alginate gel bead containing vegetable oil (ALGO), is a hydrogel bead and its buoyancy is attributable to vegetable oil held in the alginate gel matrix. The model drug, metronidazole (MZ), contained in ALGO was released gradually into artificial gastric juice, the release rate being inversely related to the percentage of oil. The second, alginate gel bead containing chitosan (ALCS), is a dried gel bead with dispersed chitosan in the matrix. The drug-release profile was not affected by the kind of chitosan contained in ALCS. When ALCS containing MZ was administered orally to guinea pigs, it floated on the gastric juice and released the drug into the stomach. Furthermore, the concentration of MZ at the gastric mucosa after administration of ALCS was higher than that in the solution, though the MZ serum concentration was the same regardless of which type of gel was administered. These release properties of alginate gels are applicable not only for sustained release of drugs but also for targeting the gastric mucosa.     

Alginate microspheres of isoniazid for oral sustained drug delivery

In the present study, spherical microspheres able to prolong the release of INH were produced by a modified emulsification method, using sodium alginate as the hydrophilic carrier. The shape and surface characteristics were determined by scanning electron microscopy using gold sputter technique. Particle sizes of both placebo and drug-loaded formulations were measured by SEM and the particle size distribution was determined by an optical microscope. The physical state of the drug in the formulation was determined by differential scanning calorimetry (DSC). The release profiles of INH from microspheres were examined in simulated gastric fluid (SGF pH 1.2) and simulated intestinal fluid (SIF pH 7.4). Gamma-scintigraphic studies were carried out to determine the location of microspheres on oral administration and the extent of transit through the gastrointestinal tract (GIT). The microspheres had a smoother surface and were found to be discreet and spherical in shape. The particles were heterogeneous with the maximum particles of an average size of 3.719mum. Results indicated that the mean particle size of the microspheres increased with an increase in the concentration of polymer and the cross-linker as well as the cross-linking time. The entrapment efficiency was found to be in the range of 40-91%. Concentration of the cross-linker up to 7.5% caused increase in the entrapment efficiency and the extent of drug release. Optimized isoniazid-alginate microspheres were found to possess good bioadhesion (72.25+/-1.015%). The bioadhesive property of the particles resulted in prolonged retention in the small intestine. Microspheres could be observed in the intestinal lumen at 4h and were detectable in the intestine 24h post-oral administration, although the percent radioactivity had significantly decreased (t(1/2) of (99m)Tc=4-5h). Increased drug loading (91%) was observed for the optimized formulation suggesting the efficiency of the method. Nearly 26% of INH was released in SGF pH 1.2 in 6h and 71.25% in SIF pH 7.4 in 30h. No significant drug-polymer interactions were observed in FT-IR studies. Dissolution and gamma-scintigraphy studies have shown promising results proving the utility of the formulation for enteric drug delivery.     

Biodegradable alginate microparticles developed by electrohydrodynamic spraying techniques for oral delivery of protein

In this study, alginate microparticles were prepared by cross-linking alginate with calcium chloride solution using an electrohydrodynamic spraying technique. The effects of alginate and calcium chloride concentration as well as electrical potential on particle size and shape were investigated. The results showed that 1 mg ml^?1 alginate medium viscosity (AMV), 2.5 mg ml^?1 CaCl₂, electrical potential 18 kV (F1) and 0.5 mg ml^?1 alginate low viscosity (ALV), 2.5 mg ml^?1 CaCl₂, electrical potential 20 kV (F2) yielded the spherical shape and small particles of 937 ± 158 nm and 1556 ± 51 nm, respectively. In bovine serum albumin (BSA) entrapment efficiency study, initial BSA of 5, 10, 20, 40 and 60% w/w to polymer was incorporated into these alginate microparticles. The results revealed that F2 with initial BSA 10% w/w showed the highest entrapment efficiency of 49.70 ± 0.01%. The result of BSA content revealed that F2'with the initial BSA of 20% w/w showed the highest amount of BSA content of 3.92 ± 0.02 mg g^?1 of particles. F1 and F2 with the initial BSA of 5%, 20% and 40% w/w were chosen to evaluate for the release in PBS pH 7.4. It was found that F1 with the initial BSA of 40% w/w showed the slowest release rate and sustained release. The release of F1 in 0.1 N HCl solution (pH 1.2) was slower than that in pH 7.4. This electrohydrodynamic spray technique (EHDA) can be applied to prepare alginate in micro size and can encapsulate BSA. Alginate microparticles can further be optimized for oral delivery of several pharmaceutical peptides and proteins.     

Recent advances and perspectives on coated alginate microspheres for modified drug delivery

BACKGROUND: Alginate microspheres represent a useful tool for modified drug delivery. Their preparation is quite easy and is usually based on the gelling properties of the polysaccharide in the presence of divalent ions; nevertheless, microparticles prepared only with calcium alginate show several problems, mainly related to the mechanical stability and to the release that, in most cases, is too fast. To overcome such inconveniences, polymer-coated alginate microspheres and/or appropriately interpenetrating polymer network (semi-IPNs and IPNs) structures formed with alginate and other macromolecules were developed. OBJECTIVE: This article reports a synthetic overview on the most recent searches carried out on coated alginate microspheres. METHODS: After a section focused on the microsphere preparation, this article is divided into several main topics related to the specific polymer that was used as a coating material to provide a rationale in reporting literature data. In the last section, the advantages and disadvantages of the various approaches are discussed and the authors' opinion on perspectives for further studies and novel applications of coated alginate microspheres are reported. CONCLUSION: Ca(2+)-alginate microparticles could experience a new era if scientists will increase their efforts in developing microparticles with smart properties.     

Propellant-driven aerosols for delivery of proteins in the respiratory tract.

Metered-dose propellant-driven aerosols of an antigenically reactive protein were produced by combining bovine gammaglobulin (BGG) with one of several surfactants soluble in Freon or dimethylether propellants. Small-particle protein aerosols were most effectively produced by lyophilizing surfactants and proteins prior to the addition of propellants. Up to 26% of the total aerosolized protein was of respirable size. Aerosol metering valves delivering small volumes were most effective in producing respirable-sized (< or = 4 micron median mass aerodynamic diameter) protein aerosols. Proteins were suspended in liquified propellants as both propellant-soluble molecules and visible sedimenting clusters which both contributed to making respirable-sized protein aerosol particles. Electron microscopy showed that respirable-sized protein particles were composed of variable-sized chain aggregates of spherical subunits. Proteins were antigenic after suspension in liquified propellant and release as aerosols, but antigenicity diminished with extended propellant exposure. Local immunity in the respiratory tract is a key factor in resistance to respiratory infections. Metered-dose propellant-driven aerosols offer a potentially attractive method for delivering small-particle aerosols of immunizing antigens or other therapeutic proteins to the respiratory tract.     

Sodium alginate microspheres of metoprolol tartrate for intranasal systemic delivery: development and evaluation

Bioadhesive sodium alginate microspheres of Metoprolol tartrate (MT) for intranasal systemic delivery were prepared to avoid the first-pass effect, as an alternative therapy to injection, and to obtain improved therapeutic efficacy in the treatment of hypertension and angina pectoris. The microspheres (Ms) were prepared using emulsification--cross-linking method. The formulation variables were drug loading, polymer concentration, cross-linking agent concentration, and cross-linking time. The Ms were evaluated for characteristics, like particle size, incorporation efficiency, swelling ability, in vitro bioadhesion, in vitro drug release, and in vivo pharmacodynamic performance in rabbits against isoprenaline-induced tachycardia. Treatment of in vitro data to different kinetic equations indicated matrix-diffusion controlled drug delivery from sodium alginate Ms. Polymer concentration, cross-linking agent concentration, and cross-linking time influenced the drug release profiles significantly. In vivo studies indicated significantly improved therapeutic efficacy of MT from Ms with sustained and controlled inhibition of isoprenaline-induced tachycardia as compared with oral and nasal administration of drug solution.     

Effects of alginate coated on PLGA microspheres for delivery tetracycline hydrochloride to periodontal pockets

The effects of alginate coated on tetracycline (Tc) loaded poly (D, L-lactic-co-glycolic acid) (PLGA) microspheres fabricated by double emulsion solvent evaporation technique for local delivery to periodontal pocket were investigated. Alginate coated PLGA microspheres showed smoother surface but enlarged their particle sizes compared with those of uncoated ones. In addition, alginate coated microspheres enhanced Tc encapsulation efficiency (E.E.) from 11.5 +/- 0.5% of uncoated ones to 17.9 +/- 0.5%. Moreover, all of the coated PLGA microspheres even fabricated at different conditions could prolong Tc release from 9-12 days with 50% or higher in cumulative release of Tc compared with those of uncoated ones. The swelling ratios of PLGA microspheres for alginate coated or uncoated ones, one of the possible mechanisms for enhancing Tc release for the coated ones, were measured. The results showed that 20% or higher in swelling ratio for the coated microspheres at the earlier stage of hydration (e.g. < or = 24 h) could be an important factor to result in high Tc release compared to the uncoated ones. In conclusion, alginate coated Tc loaded PLGA microspheres could enhance Tc delivery to periodontal pocket by enhancing drug encapsulated efficiency, released quantities and sustained release period compared with uncoated ones.     

Effects of alginate coated on PLGA microspheres for delivery tetracycline hydrochloride to periodontal pockets

The effects of alginate coated on tetracycline (Tc) loaded poly (D, L-lactic-co-glycolic acid) (PLGA) microspheres fabricated by double emulsion solvent evaporation technique for local delivery to periodontal pocket were investigated. Alginate coated PLGA microspheres showed smoother surface but enlarged their particle sizes compared with those of uncoated ones. In addition, alginate coated microspheres enhanced Tc encapsulation efficiency (E.E.) from 11.5?±?0.5% of uncoated ones to 17.9?±?0.5%. Moreover, all of the coated PLGA microspheres even fabricated at different conditions could prolong Tc release from 9–12 days with 50% or higher in cumulative release of Tc compared with those of uncoated ones. The swelling ratios of PLGA microspheres for alginate coated or uncoated ones, one of the possible mechanisms for enhancing Tc release for the coated ones, were measured. The results showed that 20% or higher in swelling ratio for the coated microspheres at the earlier stage of hydration (e.g.?≤?24?h) could be an important factor to result in high Tc release compared to the uncoated ones. In conclusion, alginate coated Tc loaded PLGA microspheres could enhance Tc delivery to periodontal pocket by enhancing drug encapsulated efficiency, released quantities and sustained release period compared with uncoated ones.     

Preparation and evaluation of alginate-chitosan microspheres for oral delivery of insulin

The alginate-chitosan microspheres with narrow size distribution were prepared by membrane emulsification technique in combination with ion (Ca²⁺) and polymer (chitosan) solidification. The preparation procedure was observed, and the physical properties (particle size distribution, surface morphology, chitosan distribution, zeta potential) of the microspheres were characterized. Subsequently, the microspheres were employed to load model peptide of insulin. The effect of loading ways on the loading efficiency and immunological activity of insulin were investigated. It was shown that the higher loading efficiency (56.7%) and remarkable activity maintenance (99.4%) were obtained when the insulin was loaded during the chitosan solidification process (Method B). Afterward, the release profile in vitro for the optimal insulin-loaded microspheres was investigated. Under the pH conditions of gastrointestinal environment, only 32% of insulin released during the simulated transit time of drug (2 h in the stomach and 4 h in the intestinal). While under the pH condition of blood environment, insulin release was stable and sustained for a long time (14 days). Furthermore, the chemical stability of insulin released from the microspheres was well preserved after they were treated with the simulated gastric fluid containing pepsin for 2 h. Finally, the blood glucose level of diabetic rats could be effectively reduced and stably kept for a long time (∼60 h) after oral administration of the insulin-loaded alginate-chitosan microspheres. Therefore, the alginate-chitosan microspheres were found to be promising vectors showing a good efficiency in oral administration of protein or peptide drugs.     

Stabilizing effects of calcium alginate microspheres on Mycobacterium bovis BCG intended for oral vaccination

In this study, alginate microspheres containing BCG were prepared at a diameter of approximately 10 microm by emulsification-internal gelation of an alginate-BCG solution dispersed in olive oil using a high rate speed stirrer. The stability of BCG was assayed at 4 degrees C showing that the encapsulated BCG was more stable than free BCG at least for 5 weeks; however, BCG in sodium alginate solution was not stable at all. On the other hand, the studies using media with different pH (1.2, 4.4, 6.2, 6.8 and 7.5) have demonstrated that the alginate microspheres are stable in acidic medium for upto 1.5 h without any sign of disintegration. Moreover, BCG incorporated in alginate microspheres demonstrated an almost 9-fold increase in viable bacilli in simulated gastric fluid (SGF) after 1.5 h in comparison with free BCG.     

Stabilizing effects of calcium alginate microspheres on mycobacterium bovis BCG intended for oral vaccination

In this study, alginate microspheres containing BCG were prepared at a diameter of ～10?µm by emulsification–internal gelation of an alginate–BCG solution dispersed in olive oil using a high rate speed stirrer. The stability of BCG was assayed at 4°C showing that the encapsulated BCG was more stable than free BCG at least for 5 weeks; however, BCG in sodium alginate solution was not stable at all. On the other hand, the studies using media with different pH (1.2, 4.4, 6.2, 6.8 and 7.5) have demonstrated that the alginate microspheres are stable in acidic medium for upto 1.5?h without any sign of disintegration. Moreover, BCG incorporated in alginate microspheres demonstrated an almost 9-fold increase in viable bacilli in simulated gastric fluid (SGF) after 1.5?h in comparison with free BCG.